The present invention relates to a method and apparatus for making a can body, more particularly to a method and apparatus for making a can body by jointing the side edges of a can body preform formed from a ferromagnetic metal sheet such as tinplate.
A can body having a side joint usually has been manufactured by forming a can body preform having an overlapped portion by overlapping the opposite edges of a metal blank of such as tinplate, and then welding or bonding with an adhesive the overlapped portion. The can body of this type has a step along the side joint, and thus is disadvantageous in that it is difficult to mend satisfactorily the joint with lacquers or the like and ensure hermetic sealability of the double-seamed portions of a can formed by double seaming top and bottom ends to the can body.
An art of making a can body by joining, preferably laser beam welding, the confronting side edges in edge-to-edge relationship without overlap is proposed in U.S. Pat. No. 4,152,573. In case of joining, particularly welding of this type, it is necessary to joining or welding the confronting edges in such abutting relationship that the edge faces thereof are in close contact with each other without substantial gap and step therebetween along the whole length, so as to obtain a joint or weld which has a thickness substantially equal to that of the metal sheet and is free of the step and pinholes.
It is, however, very difficult to bring the confronting edge faces of a relatively thin metal sheet blank of such as tinplate, usually of 0.15 to 0.25 mm thick into the above-mentioned abutting relationship.
Accordingly, in the aforementioned prior art the confronting side edges are clamped by means of two longitudinal parallel vices which are pressed together with clamping screws, so as to ensure the abutting relationship free of the gap and the step, that is, to avoid the possibility of creating pinholes and a surplus thickness at the weld.
This type of butt-joining or butt-welding is poor in productivity and unsuitable to a high speed production of the can body such as several hundreds can bodies per minute, since the confronting edges of the respective can body preform must be clamped by screwing, which is time-consuming.